Together with joint venture partners Talos Energy and Sierra Oil & Gas, Premier said its Zama-1 well's initial gross original oil in place estimates were in excess of 1bn barrels, which could extend into a neighbouring block.
"The team deserves a great deal of credit for their conviction in this opportunity and their leadership in making Talos the first private sector operator to receive acreage and drill a successful offshore exploration well in Mexico following the landmark energy reforms of 2014". Medina called Zama "one of the 20 largest shallow-water fields discovered globally in the past 20 years".
Premier Oil and its partners have announced a "world class" discovery of up to two billion barrels of oil off the coast of Mexico.
Premier Oil's Chief Executive Tony Durrant said the discovery "adds materially" to Premier's portfolio of assets.
He added: "We believe that this discovery represents exactly the objectives of energy reform: new capital, new participants and a spirit of ingenuity that will generate new local jobs and income for the Mexican government".
The well, where drilling began May 21, is located 60.5 kilometers from the port of Dos Bocas, Tabasco, in a 166 meter water link.
Riverstone said that preliminary analysis indicates the presence of a contiguous oil bearing interval of over 1,100 feet - or 335 meters - gross, with net pay of over 650 feet and no identified oil-water contact.
In addition, initial tests reveal that light oil has been recovered to the surface of the area.
Talos is a technically driven independent exploration and production company focused on the exploration, development and acquisition of oil and natural gas.
In March this year, Italy's oil major Eni drilled the first well by an global oil company in Mexican waters, and said the well indicated a "meaningful" volume of oil.
Sierra owns 40 per cent of the block, Talos has 35 per cent and Premier 25 per cent, which sent Premier oil shares up as much as 25 percent during early Wednesday morning trading.